"And now I say unto you,
Refrain from these men, and let them alone: for if this
counsel or this work be of men, it will come to nought:
39 But if it be of God, ye cannot overthrow it, lest
haply ye be found even to fight against God". 40 And
to him they agreed:...

You have not overthrown Christianity, Despite your best
efforts to do so over the last two thousand years,
(Gamaliel said that it would come to nought without
these efforts) so according to Gamaliel, it is of God.